The invention is related to providing a safety seat belt retractor including a self-locking belt shaft for winding a web, and particularly, to providing a skid mechanism mounted on a web winding shaft for limiting the torque of a torsion bar in multi-stages to smoothly control the tension of a belted occupant.
In general, a seat belt retractor is provided with a belt winding shaft or reel of which a seat belt or web is wound around, in which the belt winding shaft includes a torsion bar that is connected at one end thereto and at the other end to a blocking member of the retractor. Therefore, the seat belt retractor comprising the torsion bar is rotated at one end and locked at the other end in an emergency situation to force it to be twisted, thereby absorbing the impact energy of the occupant. Particularly, when the torsion bar is used in connection with an air bag, the response of the torsion bar allows for an additional, but decelerated forward displacement of the belted occupant. In other words, as the belt unwinds from the belt shaft in an emergency situation, the belt loading of the belt shaft blocked by the blocking member is reduced by the torsion bar which yields and allows for further rotation of the belt shaft.
However, the average seat belt retractor has disadvantages in that the torsion bar may be excessively twisted and broken due to the higher withdrawal force of the seat belt in an emergency situation when a vehicle collides with another vehicle or the weight of the belted occupant is too great Also, the acting force applied to the belt shaft is increased by the torsion bar as a result of the cold deformation of the material and the decreasing winding diameter. In other words, as a result of the associated lever arm reduction, the associated force-path characteristic curve is progressive.
In order to resolve this problem, there are two typical patents that have been registered U.S. Pat. No. 4,322,046 and the other is International Publication No. WO96/32303.
The former patent discloses a seat belt retractor comprising a reel, a torsion bar, one end of which is connected to a reel and is rotated therewith and the other end of which is locked during an emergency, and a stopper including a screw member which moves together with the reel when the reel rotates the torsion bar while twisting due to the tensional force of the seat belt and which is stopped after moving at a predetermined distance to prevent the reel from rotating. The torsion bar includes a bar-shaped twisting portion accommodated within the reel with one end being connected to the reel, a screw portion provided with a screw in the outer periphery thereof, which is formed at the other end of the twisting portion and has a larger diameter than that of the twisting portion, and a gear portion mounted on the screw portion so as to enable the screw motion therewith towards the stopping member with the reel, in which the twisting portion is integrally connected to the screw portion and the gear portion. Therefore, the torsion bar is not broken even by the greater tensional force of the seat belt.
But, the patent fails to adjust the torque of the torsion bar due to the sudden withdrawal of the seat belt upon the emergency coupling of a vehicle sensor such as a pendulum with the gear portion. It means that the screw of the screw portion is distorted under the influence of the twisting portion, thereby making it difficult to move the screw member on the screw. Further, the performance of relieving the restraining force of an occupant due to the belt withdrawal stopping state in an emergency deteriorates.
The latter patent provides a belt roller with a damping force limiter for restricted belt withdrawal, when a blocking member is engaged. The damping force limiter comprises a tension rod connected at one end to a belt winding shaft and at the other end to a blocking member of its end, a profile head connected to the associated shaft end face which rotates together with the belt winding shaft and an energy dissipating structure provided in the force transmission path including the torsion rod, the profile head and the shaft.
FIG. 1 is an exploded perspective view of a belt roller provided with a damping force limiter. The belt roller comprises an U-shaped housing 10, in whose U-limbs or the aperture 12 arranged therein a belt winding shaft 13 is mounted. At the blocking end of the belt winding shaft 13, a profile head 14 rotating with the end face of the belt winding shaft 13 is associated with the end face of the belt winding shaft 13. A blocking member 15 is mounted on the profile head 14, which can be radially deflected under the action of a control device and which is controlled so as to be guided into the toothing 30 arranged in the associated aperture in the event of deceleration.
The profile head 14 and the belt winding shaft 13 are connected to one another by a torsion rod 16 acting as a force limiting device, the connection being formed in that one end of the torsion rod 16 is connected preferably in a positive-locking manner to the profile head 14, and the other end of the torsion rod 16 extending in the belt winding shaft 13 is connected to the belt winding shaft 13 in a manner not shown. If, after the blocking of the profile head 14 by means of the blocking member 15, there is a further belt extraction with a corresponding rotation of the belt winding shaft 13, then this rotational movement is transmitted via the torsion rod 16 with a simultaneous absorption of energy to the profile head, either an abutment being provided between the belt winding shaft 13 and the profile head 14 to limit the deformation of the torsion rod 16 or the torsion rod being constructed in such a manner that it can carry out a larger number of rotations than is required for the energy conversion. In order to provide the additional, energy-dissipating structure in the transmitting path, at least one shearing element 25 or 31 is provided at the end face of the belt wind shaft 13 facing the profile head 14, which shearing element engages in an associated bore 26 in the profile head 14. By means of the cross-sectional surface area of the shearing element and its distance from the pivot axis of the belt winding shaft 13 or profile head 14, it is possible to adjust the torque and path in such a manner that the shearing element shears off and thus the sole loading of the torsion rod 16 is effected. After the shearing off of the shearing element, the torque is exclusively transmitted by the torsion rod 16.
But, the patent also fails to adjust the torque of the torsion rod after the shearing off of the shearing element due to the excessive drawing force of a web in the event of loading. The reason is because the shearing off of the shearing element means that the torsion rod 16 rotates only one time for the adjustment of the torque. Due to further rotation of the torsion rod beyond the inheritance stress limit, the torsion rod may cause its breaking. And also, the effect of the damping force gets lost, thereby resulting in an occupant being under the undesirable strong tension influence of the web during an emergency, because the profile head cannot be rotated in itself to the initial position upon the returning of the torsion rod to the original state due to the removal of the web loading.
Therefore, it is very desirable that the torque of a torsion bar be smoothly adjusted or controlled under the condition that the torsion bar is not broken. Also, it is further preferable to control the torque of the torsion bar in multi-stages.
One object of the invention is to provide a skid mechanism of a safety belt retractor for limiting the torque of a torsion bar to smoothly control the tension of a belted occupant.
Another object of the invention is to provide a skid mechanism of a safety belt retractor for limiting the torque of a torsion bar in multi-stages to increase the limiting quantity of the damping force.
Still another object of the invention is to provide a skid mechanism of a safety belt retractor for enabling it to return to its original position upon relieving the twisting of the torsion bar.